DESCRIPTION (Investigator's Abstract): The family of human diseases termed amyloidoses have the common feature that naturally occurring, normally innocuous soluble peptides or proteins assemble into particularly stable insoluble polymers which accumulate, increase in size, and eventually cause pathological damage to surrounding tissue. Growth of the amyloid deposits (defined by a particular regular structure which favors binding of certain dyes) is the hallmark pathological process of these untreatable diseases, but is poorly understood. Two major hurdles have frustrated researchers attempting to understand the process of amyloid deposition in most of these diseases. The first is a lack of relevant model systems for the process, and the second is that the amyloid monomers and polymers have resisted high resolution determination of their three dimensional structures. We have chosen to focus our study of the molecular structural correlates of amyloid growth in one particular nervous system amyloidosis, Alzheimer's disease (AD), but a detailed knowledge of the deposition process in this ailment should have implications for other amyloidoses. Recently we have developed a novel assay for in vitro deposition of the Beta- amyloid peptide of AD (Beta A4) onto amyloid deposits in unfixed human tissue AD under physiological conditions. This advance has allowed us to examine activity as a function of primary sequence and identify forms of the monomer peptide which fully support plaque growth but are amenable to high resolution structure determination by nuclear magnetic resonance spectroscopy in water. We propose here to determine the kinetics of amyloid peptide deposition onto and dissociation from tissue plaques and to determine the conformation of B-amyloid peptides under conditions where they do and do not support plaque growth. The combination of structural and kinetic studies will identify important conformational features involved in amyloidosis and illuminate for the first time at high resolution an important therapeutic target. Most important, it will allow construction of specific testable hypotheses about structure and activity in amyloidosis.